The evidence mounts about Iran's clandestine nuclear-weapons ambitions — including a new uranium enrichment facility that President Obama revealed at the G-20. There is now evidence that the U.S. may be preparing a weapon that could be used on nuclear facilities in Iran. The Pentagon requested, and Congress quietly approved, more than $50 million for a 30,000-pound bomb, known as the Massive Ordnance Penetrator. The bunker-buster is capable of hitting reinforced targets 200 feet underground — exactly the type of weapon that could destroy one of these nuclear facilities. So tonight, we ask: Would an attack with this weapon be a wise strategy in the showdown with Iran? Tell us what you think. You can follow "Nightline" anytime on Twitter: http://twitter.com/Nightline.